1. Field of the Invention
The invention relates to the fabrication of metal-oxide-semiconductor (MOS) field-effect transistors.
2. Prior Art
Various techniques have been used to implant the channel regions of MOS transistors to control short channel effects or to change other characteristics. One commonly used technique is a so called "halo" implant, where ions opposite in conductivity type to that used for the source region and drain region are implanted adjacent to these regions. These highly doped regions provide a higher punchthrough resistance including higher resistance to drain induced barrier lowering.
Often in the prior art the dopant for the halo regions is implanted with the wafer tilted after the gate is formed. This is shown in "A New Half-Micron p-Channel MOSFET with LATIPS (LArge-Tilt-Angle Implanted Punchthrough Stopper), by Hori and Kurimoto, IEDM 88, beginning at page 394.